The present invention relates to composite labels useable at high temperatures temperatures above about 400xc2x0 C.). More particularly, the present invention relates to high temperature composite labels in which the label body includes a glassy phase and a refractory phase, and in which an optically discernible code pattern is, or can be, formed in a label top layer.
Parts and products can be tracked during manufacturing and marketing operations in order to facilitate commodity distribution, customizing product features, process control, stock control, sales control, quality control, and the like. Such tracking requires some means for marking or labeling parts and products so that such parts and products can be readily and accurately identified during tracking. For example, according to one approach, a label bearing identification information in human readable form (e.g., alphanumeric information) or machine readable form (e.g., bar code information), or both, is attached to parts running on a production line. The label is read at one or more process stations so that specific operation steps can be carried out according to work schedules corresponding to the identification information.
In some industries, printed paper labels are used for tracking purposes. However, for other industries, (e.g., steel making industries and cathode ray tube industries) production lines operate at temperatures well above ambient conditions (e.g., above 250xc2x0 C., or even above 400xc2x0 C.). For example, the manufacture of a glass cathode ray tube typically involves temperatures in the range from about 400xc2x0 C. to about 1000xc2x0 C. Paper labels do not survive at these temperatures. Consequently, labels that can be easily attached to parts and maintain their integrity at such temperatures are needed.
Many parts have nonplanar surfaces to which a label is attached in order for such parts to be tracked. For example, a cathode ray tube includes a glass cone component and a glass faceplate component, both of which have curved, nonplanar surfaces. Consequently, not only is there a need for temperature resistant labels, but there is also a need for temperature resistant labels which are conformable to nonplanar substrates at application temperatures.
Another concern relates to the durability of labels. It is most desirable if a label is durable enough to survive the entire production process without requiring interim replacement. Unfortunately, many of the previously known labels adapted for high temperatures become disfigured and/or unreadable too easily and must be replaced several times during production in order to preserve tracking capabilities. Other labels, although durable, have a tendency to delaminate and fall off of their substrates. Consequently, labels with both excellent durability and tenacious bonding characteristics would be desirable.
As a practical matter, production yields seldom reach or are maintained at 100%. For example, parts can break, fail to meet specifications, or suffer from other defects that necessitate discarding or recycling of the parts. Recycling is often more desirable than discarding bad parts, particularly when the raw materials incorporated into the parts are relatively expensive. However, before recycled materials can be returned to the production line, contaminants are preferably removed to maintain the quality of parts formed from recycled material. Unfortunately, many of the previously known labels would contaminate the recycled supply and must be removed. Labels comprising heavy metal atoms such as Pb, Hg, As, Co and Cr(VI), whether present in pure form or in the form of oxides, are of particular concern due to the toxicity associated with such materials. Oxides of heavy metals such as Pb, Cd, Hg, and/or As are known to be incorporated into glassy phases as one approach for achieving low softening points (e.g., softening points below about 350xc2x0 C.). Oxides of heavy metals such as Co and Cr are known to be used for providing black color. Consequently, articles having a label comprising one or more these heavy metals are typically recycled by delabeling and separating the less desirable heavy metals containing labels from the articles. These steps can be costly and/or extremely difficult, particularly if the bond between the article and the label is especially tenacious. In addition, heavy metals may be dispersed in air when the labels containing such metals are heated to high temperatures. Accordingly, it would be desirable to provide a label substantially free of these heavy metal atoms.
In one aspect, the present invention provides a composite material (typically a ceramic composite) suitable for labeling a substrate, comprising:
(a) a fired ceramic body comprising a base layer, the base layer including:
(i) a first glassy phase;
(ii) a first refractory phase (preferably a ceramic material such as particulate ceramic material) interspersed with the first glassy phase,
the first glassy phase being capable of wetting a substrate at an application temperature; and
(b) a top layer provided on the fired ceramic body,
wherein there is sufficient color contrast between the top layer and the fired ceramic body such that a code pattern (preferably formed by selectively removing the top layer from portions of the composite layer) is optically discernible. Optionally, a label according to the present invention may further comprise a translucent (including transparent or clear) cover (e.g., a protective layer or a coating) over the top layer. A protective layer (e.g., a glass layer) is sufficiently translucent to allow a bar code reader, human eye, or other detector means to view or read the underlying code pattern. Optionally, the translucent layer(s) is a fugitive material.
Embodiments of labels according to the present invention are capable of retaining not only their dimensional integrity, but also the integrity of information incorporated into the labels, especially when the label is exposed to high temperatures (e.g., temperatures above 250xc2x0 C., preferably 400xc2x0 C. to 1000xc2x0 C.). In another aspect, labels according to the present invention can be conveniently applied to a wide range of substrates, including metal, glass, ceramics, and the like, which are intended to be used at relatively high temperatures.
Labels according to the present invention comprise a top layer of one color overlying a layer of a contrasting color. When portions of the top layer are selectively removed to expose portions of the underlying layer, the color contrast between layers allows the resultant pattern formed from the top layer to be optically discernible. This allows information to be incorporated into the label by selectively patterning or removing the top layer to form one or more symbols of a code pattern either as a negative or a positive image, as desired. Such a code pattern, in turn, allows a labeled substrate to be easily identified and tracked during production. The code pattern(s) can be formed in the label either before and/or after the label is attached to a corresponding substrate. Information can be incorporated into the label one or more times during the service life of the label as well. This is particularly advantageous for production operations in which updating label information during the course of production is desired.
The code pattern incorporated into the label may be human readable, machine readable, combinations of these, and the like. In preferred embodiments, the code pattern includes human readable alphanumeric characters, machine readable bar code characters, or combinations thereof Bar code patterns, in particular, can be easily and rapidly formed in labels of the present invention using, for example, well known laser ablating techniques.
Because of the color contrast and multilayer construction of labels according to the present invention, code patterns can be formed by abrasion, etching or abrading techniques in which substantially only portions of the top layer are removed. In other words, material can be selectively removed from the label only to a depth substantially corresponding to the thickness of the top layer. Very little if any of the underlying label layers need be subjected to such removal, and the substrate itself remains unaltered. Advantageously, therefore, the underlying layers of the label can further serve as a protective barrier between the patterning applied to the top layer and the substrate below. In this way, the substrate can be protected from damage that might otherwise occur if such patterning techniques were to be applied directly to the substrate itself In another aspect, the code pattern can be formed directly, for example, by depositing the pattern to the top layer using a surface printing technique such as ink jet printer with a ceramic oxide containing ink or depositing the composition through a mask.
Labels according to the present invention include a structural base layer incorporating both a glassy phase and a refractory phase. This composite structure makes it easy to firmly attach the labels to a wide variety of substrates at an application temperature at which the glassy phase liquifies and wets the substrate surface. Because the glassy phase itself bonds to the substrate, no other adhesives are required to achieve label attachment. When the glassy phase is liquified at the application temperature, the refractory phase structurally and dimensionally supports the base layer. Simultaneously, the base layer can be pliable due to the presence of the melted glassy phase, thereby allowing the label to conform to nonplanar substrates, while the presence of the reinforcing refractory phase allows the label to retain its dimensional and structural integrity as the label is flexed, bent, or otherwise shaped to conform to such a substrate.
In applications in which the substrate is formed from a glass and/or a crystalline ceramic, the coefficient of thermal expansion of a label of the present invention can generally be matched as closely to the coefficient of thermal expansion of the substrate as desired. Matching the coefficients of thermal expansion of the substrate and label offers numerous advantages. For example, such matching enhances the strength of the bond between the label base layer and the substrate. As a further advantage, such matching minimizes thermally induced stresses between the substrate and label as temperatures change. If the coefficients of thermal expansion are not matched well, thermal induced stresses can damage the label and/or the substrate.
In preferred embodiments, labels according to the present invention preferably include substantially no heavy metal atoms selected from Pb, Cd, As, Hg, Co, and Cr(VI). Such heavy metal atoms generally pose environmental and/or health hazard so that avoiding the use of such materials is highly desirable. Providing labels that are free of these kinds of heavy metal atoms also facilitates recycling, because both the label and the substrate can be processed for recycling together without having to remove the label. If the label were to incorporate these kinds of heavy metal atoms, the label might be an undesirable contaminant that would have to be removed from the substrate in the event recycling is desired. This would involve extra expense and processing steps. Avoiding such heavy metal atoms as label constituents is particularly advantageous for industrial applications such as the manufacture of cathode ray tubes, where breakage is known to occur and recycling is regularly practiced.
Another aspect of the present invention relates to a labeled cathode ray tube, or components thereof (e.g., faceplates and funnels). The labeled cathode ray tube comprises a cathode ray tube glass surface and at least one fired composite label according to the present invention attached to the cathode ray tube glass surface.
In yet another aspect, the present invention provides a method of applying a label (including a blank label (i.e., a label without the code pattern)) according to the present invention to a substrate, the method comprising the steps of,
(a) providing and/or heating a substrate (e.g., a ceramic material) at and/or to an application temperature; and
(b) attaching the label to the substrate such that the first glassy phase of the label bonds to the substrate.
Optionally, the label is heated to and/or is at the application temperature rather than the substrate, or both the substrate and the label are heated to and/or are at the application temperature.
In this application:
xe2x80x9cSoftening pointxe2x80x9d refers to the temperature at which the viscous flow of a glassy composition counteracts thermal expansion as determined according to ASTM test method E 1545-95A (December, 1995) entitled xe2x80x9cStandard Test Method for Assignment of Glass Transition Temperature by Thermomechanical Analysis,xe2x80x9d the disclosure of which is incorporated herein by reference. Such a temperature generally corresponds to the maximum point on a thermal expansion curve. In this method, the softening point is referred to as the xe2x80x9cdilatometricxe2x80x9d softening point.
xe2x80x9cCeramicxe2x80x9d refers to an inorganic, nonmetallic material, such as metal oxides, metal nitrides, and metal oxynitrides, preferably consolidated by the action of heat.
xe2x80x9cFiredxe2x80x9d refers to densification or consolidation by action of heat.
xe2x80x9cRefractoryxe2x80x9d refers to a material that maintains its structural integrity at temperatures at least up to about 1000xc2x0 C.
xe2x80x9cGlassyxe2x80x9d refers to an amorphous inorganic oxide material having a softening point above which the material melts or softens. Amorphous materials typically have a diffuse x-ray diffraction pattern without definite lines that might otherwise indicate the presence of a crystalline phase.